Method of protecting metal surfaces from corrosion and corrosion inhibitor compositions



United States l aterit O METHOD OF PROTECTING METAL SURFACES FROM CORROSION AND CORROSION INHIBI- TOR COMPOSITIONS Frank W. Pfohl, Westmont, Ill., and Vance P. Gregory,

Elsmere, Del., assignors to Armour and Company, Chicago, 111., a corporation of Illinois No Drawing. Application July 23, 1952, Serial No. 300,488

Claims. (Cl. 106-14) This invention relates to a method of protecting metal surfaces from corrosion and to corrosion inhibitor compositions.

It is a general object of this invention to provide a novel method for protecting metal surfaces from corrosion involving the use of a class of corrosion inhibitors whose unexpectedly superior corrosion inhibiting properties were discovered in the course of the experimental Work leading to the present invention. More specifically, it is an object of this invention to provide a method and a means for protecting ferrous metal surfaces against corrosion by the action of oxygen and water. In this connection, it is an object of this invention to provide a corrosion inhibiting method which is capable of protecting ferrous metal surfaces which are normally in contact with atmospheric air, and also ferrous metal surfaces which are normally or at least periodically in contact with liquids containing dissolved water, oxygen and other corrosive compounds or elements. It is a still further object of this invention to provide corrosion inhibitor compositions for use in the method of this invention, and

particularly corrosion inhibitor compositions in which the liquid or solid carrier for the corrosion inhibitor cooperates with the inhibitor to increase its effectiveness in protecting metal surfaces, and particularly ferrous metal surfaces. Further objects and advantages will become apparent as the specification proceeds.

It is well-known that the corrosion of metal surfaces and especially ferrous metal surfaces by the action of oxygen and water is a serious problem. One method of protecting metal surfaces against corrosion involves the treating of the surfaces with a corrosion inhibitor adsorbed onto the metal surface and forming a protective film thereon. The mechanism of action of corrosion inhibitors of this type is not entirely understood, although a number of theories have been advanced. It is known that in general organic polar compounds are adsorbed on metal surfaces, and that when adsorbed on metal surfaces they provide at least a small measure of protection for the metal surfaces. However, polar compounds differ widely in their effectiveness as corrosion inhibitors, and it is not possible in the present state of knowledge to predict that a particular organic polar compound will be even a fairly effective corrosion inhibitor under conditions of practical use. Thus, the search for better corrosion inhibitors, which is a continuing one, must necessarily be conducted largely on an empirical basis. It was therefore surprising to discover that a class of compounds and particularly a preferred group within this class are highly effective corrosion inhibitors under widely varying conditions of use, even though a much smaller amount of the inhibiting agent is employed than has generally been thought necessary with other comparable inhibiting agents.

It has been discovered that the class of compounds represented by the following structural formula can be used to effectively inhibit the corrosion of metal surfaces such as ferrous metal surfaces and to substantially acv ice complish the objects set out above. The structural formula of this class of compounds, which can be designated generically as N-aliphatic or alicyclic substituted polymethylene diamines, is as follows:

wherein R represents an aliphatic or alicyclic carbon The alicyclic or aliphatic groups bonded to one of the nitrogen atoms is preferably a resin acid or higher fatty acid residue, that is, R in the above formula is preferably an alkyl, alkylene, or resinyl radical obtained from resin or fatty acids. Either saturated or unsaturated fatty acid residues containing from 14 to 18 carbon atoms are particularly desirable. Fatty acids providing such residues can be obtained from most naturally occurring fats and oils, such as soybean oil, coconut oil, tallow, etc.

Resin acids providing resinyl radicals of the desired number of carbon atoms can be obtained from resin or tall oil. Abietic acid, which is a major component of these raw materials, is particularly desirable. Excellent results are obtained when the inhibiting agent contains a mixture of compounds in which the aliphatic or alicyclic portion of the molecules vary in chain length corresponding to the variations in chain lengths of the aliphatic or alicyclic radicals provided by naturally occurring mixtures of the resin and fatty acids. Tall oil which contains a mixture of both fatty and resin acids in roughly equal proportions can be used to produce inhibiting agents which are particularly efiective. In other words, the inhibiting agents produced from tall oil will contain a mixture of molecules in which one portion of the molecules is the hydrocarbon chain or acid residue provided by the fatty and resin acids in tall oil.

The class of compounds designated generally by the above formula, preferably contain from 2 to 6 methylene groups between the nitrogen atoms. Especially good results are obtained when the compound contains 3 methylene groups. These N-aliphatic or alicyclic substituted trimethylene diamines can be prepared by a simple and inexpensive procedure. One method which can be used is to treat the fatty or resin acids with ammonia in the presence of a suitable solvent and catalyst to produce the corresponding aliphatic or alicyclic nitrile. The nitriles can then be hydrogenated under suitable conditions to the corresponding primary amines. The primary amines can next be treated with acrylonitrile to produce the cyanoethyl aliphatic or alicyclic amines. As the final step, the cyanoethyl compounds can be hydrogenated to produce the N-aliphatic or alicyclic substituted trimethylene diamines.

The experimental work leading to this invention has' However, the presence of more than 2.

agentsis greatly increased when the compounds are employed in the form of their fatty or resin (rosin) acid salts. Salts of the character desired are simple to prepare. All that is required is that apolyamine of the type described above be mixed in the liquid phase (generally above 5.0 C.) with fatty or.resin acids. An exothermic neutralization reaction then ensues. The temperature .of the reaction is preferablykcpt below about 101)" C. Zlhe reaction products will be salts of the polyamines. At temperatures much above 100 C., the formation of amides will become excessive. When the polyamine compound :is :aJrliamine containing aprimaryand secondaryamine group as preferred,.each amine molecule can combine with .2 resin-or fatty acidmolecules. Since'the secondary nitrogen is more basicthan the primary nitrogen, .the first molecule of the .acid will probably :react with 'the secondary nitrogen, while the second molecule willreact .withx'thecprimary nitrogen. Thereforait ispreferredzto use about l-to 2 moles of fattyor resin acidsrto each mole of .diamine. For example, if a 2m 1 molar ratio of acidzto amine is employed, the resulting ;compounds will be of the type represented by the following structural formula:

wherein'R andX have the meaning previously assigned, and R'"'is an alkyl, alkylene, or alicyclic radical containing ffrom'6 to22 carbon atoms.

In preparing the diamine salts of the type illustrated in the above formula, either separate resin or fatty acids can "be used, or mixtures thereof. Naturally occurring mixtures such as those found in tall oil are particularly suitable.

I'It will be noted that the amine salts of the type illustrated by the formula above have cationic and anionic portions. 'The cationic portion is theN-aliphatic or alicyclic substituted polymethylene diamine residue with one or more additional hydrogen atoms, while the anionic portion consists of one or more fatty or resin acid molecules with the acid hydrogen removed. The fatty acid salts, and particularly the unsaturated C18 fatty acids such as oleic and linoleic, are preferred to the resin acid salts. However, good results are obtained with tall oil resin acid salts, and also mixtures of tall oil and fatty acid salts. When morethan about '2 moles of the fatty or resin acids are reactedwith one mole of the polymethylene diamine, the reaction will not go to completion. Since fatty and resin acids are in themselves slightly corrosive to metal surfaces such as ferrous metal surfaces, 'itispreferred .to form the amine salt "by reacting slightly less than two moles of acid 'to each mole of amine. However, the diacid salt is preferred to the mono-acid salt, and thereforeit is advisableto use substantially more than 1 mole of acid to each mole of diamine. Specific compounds which-have been found to 'be excellent corrosion inhibitors for ferrous metal surfaces are: N-hexadecyl-trimethylene diamine mono-oleate, N-hexadecyl-trimethylene diamine dioleate, N-octadecyl-trimethylene diamine mono-oleate, N-octadecyl-trimethylene diamine dioleate, N-tallow-trimethylene diamine mono-oleate, N-tallow-trimethylene diamine dioleate, N-soya-trimethylene diamine mono-oleate, and ,N-soya-trimethylene diamine dioleate. The oleic acid salts of the diamines are particularly advantageous because red oil (commercial grade oleic acid) is readilyavailable and inexpensive raw material. Furthermore, the employment of an unsaturated C18 fatty acid such as oleic acid tends to increase the solubility of the amine salts in oils which is desirable when the inhibiting agents are applied in oil carriers 'to the metal surfaces.

Either the diamines themselves or the diaminefatty or resin acid salts as described above can be used to inhibit corrosion of metal surfaces. In general, all that "their use'requires isthat they be applied to the metal surfaces in .metal surface.

such a way as to form an adsorbed protective film on the Since the commercial forms of most .of the diamines and diamine salts falling within the scope of this invention are normally paste-like solids, it is possible to apply them directly to the metal surfaces in solid form by spreading them over the metal surfaces to be protected or otherwise contacting the metal surfaces with the treating agent. However, this'method of applying the compounds of this invention is relatively wasteful, since corrosion inhibitors are usually added to the corrosive environment in small quantities. The inhibiting agents are preferably applied in a liquid carrier in which they are at least slightly soluble. Solvents which are suitable for this purpose include crude oil and petroleum distillates such as gasoline, kerosene, xylene, benzene, lubricating oils, etc. In general, where the metal surface is normally exposed to the atmosphere, it is preferred to apply the inhibiting agents by dissolving them in a nonpolarsolvent of relatively low volatility, since it has been found that non-polar solvents of low volatility cooperate with the treating agent in protecting the metal.surface. Hydrocarbon oils such as those employed as protective oils v(slushing oils) are excellent for this purpose. In general, hydrocarbon oils of this type have a relatively high viscosity, say from S. A. E. 20 to 80. The inhibiting agents ,of this invention can also be advantageously incorporated in hydrocarbon greases of the types employed both for protective and lubricating purposes. Geiled hydrocarbon oil greases containing bentonite or derivatives thereof can also be combined with the treating agents of this invention. Where liquids are stored in tanks or passed through pipe lines, etc. and are fairly continuously in contact with the metal surfaces of the tank walls or the pipe lines, effective inhibition of corrosion can be obtained even though the liquid in contact with the surfaces and in which the inhibiting agents are dissolved is a polar solvent such as alcohol, or is a non-polar solvent of high volatility :such as gasoline. In some solvents, such as water, the inhibiting agents are not sufiiciently soluble to permit the forming of protective films on metal surfaces by dissolving the inhibiting agents in the solvents. However, if desired emulsions of the treating agents in the water and other solvents in which the treating agents are notsoluble can be employed.

The amount of inhibiting agent which should be incorporated in the liquid carrier, preferably by dissolving therein, can .be varied widely. In general, a sufficient amount of the inhibiting agents of this invention should be dissolved in the liquid carrier to form a continuous film on the metal surface to be treated. Effective results have been obtained by incorporating as little as .0.l% by weight of the inhibiting agent in the liquid carrier. For example, the dissolving of at least .0l% by weight and preferably .05% by weight of the inhibiting agents of this invention in hydrocarbon oils which are contacted with ferrous metal surfaces for either lubricating or protective purposes has been found to almost completely prevent corrosion due to the action of water and oxygen. For use in protective hydrocarbon oils, good results are obtained for most purposes by incorporating from about .1% '10 3% of the treating agents in the protective oils. Using agreater quantity of the treating agents in liquid carriers such as hydrocarbon oils, gasoiine, etc. does not generally produce any better protective action, but does not interfere with the protective action. Therefore, if desired the agents may be added to the particular solvent to the limit of their solubility if desired. For use in lubricating and protective greases composed mainly of a gelled hydrocarbon oil, it is generally desirable to use a somewh'athi'gher proportion of the inhibiting agents. in general, f om about 1 to 5% by weight of the treating agents in the grease is desirable. However, it has been found that even bentonite greases which are susceptible to breaking of 'thegel by polar compounds, are fully compatible with the treating agents of this invention up to as much asa 50-50 mixture of the grease and the inhibiting agent.

.5 This is surprising in view of the fact that other aminetype inhibiting agents are known to break the gel of bentonite greases at concentrations as low as .1 to 1%. It can be stated in general that if the inhibiting agents are not soluble in the liquid carrier at least to .01 percent by weight, and preferably to .015 percent by weight that an effective protective film can probably not be formed on metal surfaces with the particular liquid carrier, unless special measures are taken such as emulsifying the agents in the carrier.

Adsorption type corrosion inhibitors are believed to act by the formation of a difiusion barrier on the metal surface. It is further believed that the diffusion barrier prevents or retards the diifusion of ions or molecules of the corrosive environment toward the metal surface, or prevents or retards the diffusion of metal ions into the environment. However, the exact nature of the diffusion barrier, and of its method of operation is not well understood. Experimental work leading to the present invention brought to light a number of factors which would seem to be important. It was found that the presence of two polar groups in the inhibiting agent are desirable. The adsorptive contact of both polar groups with the metal surface apparently produces a blocking eifect due to the portion of the molecule of the inhibiting agent between the two polar groups. However, not all polar groups are tenaciously enough adsorbed by ferrous metal surfaces to accomplish this result, and there appears to be a further requirement for obtaining this effect that the groups be arranged in a particular way in the molecular structure. The secondary amine polar group, and the amine-acid polar group which are present in the inhibiting agents of this invention are found to be particularly effective in forming films which tenaciously adhere to the ferrous metal surfaces. Further, the presence of the polymethylene groups between the secondary amine polar group and the amine acid polar group was found to give the desired blocking effect. Molecular models of the trimethylene diamine group of inhibitors were constructed, and it was found that both of the polar groups could probably be adsorbed on the metal surface while allowing the diamine molecule to retain a strain-free configuration. It is further believed that the effectiveness of the compounds of this invention is due in part to the fact that the portion of the molecule extending between the two polar groups is a straight chain hydrocarbon group, or specifically a polymethylene group such as a trimethylene group. This would seem to permit close packing of the molecules attached to the metal surface, which in turn is believed to produce a special orientation of the molecules into a crystal-like structure. Thus, the polymethylene portions of the molecules tend to blanket the metal surface, while the long chain fatty or resin acid groups attached to each of the polar groups are oriented approximately normal to the surface. rosion inhibition is related to close packing and orientation of the molecules of the inhibiting agent. Another way of stating this is that the eifectiveness of a diifusion barrier on a metal surface increases as its structure tends toward that of a planar crystal.

The inhibiting agents falling within the scope of this invention, and particularly the trimethylene group, are believed to have molecular structures which permit the maximizing of the desirable effects of close packing and orientation of the molecules within the adsorbed protective film. However, it has been found that the planar crystal films can be made still more effective as diffusion barriers by the action of a solvent and particularly a nonpolar solvent which cooperates with the inhibiting agents. It is believed that non-polar solvent molecules become oriented between the outwardly extending hydrocarbon chains of the inhibitor and are held there more or less firmly due to the Van der Waals forces between the hydrocarbon chains, thus completing the close packed planar crystal. If the non-polar solvent used as a liquid carrier for the treating agents is highly volatile, the pro- Apparently, cor- I 6 tective film will be impaired by the evaporation of the solvent molecules from within the planar crystal structrue on exposure of the coated metal surface to the atplanar crystal, and (2) Incorporation of the hydro carbon oil molecules of the solvent into the spaces between the hydrocarbon chains in the planar crystal, the whole forming a diffusion barrier which is firmly bonded to the metal surface.

For the purpose of demonstrating the effectiveness of the corrosion inhibiting agents of this invention in accomplishing the stated objectives, it is desired to set out the following examples reporting actual tests of the inhibiting agents.

Example I N-tallow-trimethylene diamine, N-tallow-trimethylene diamine mono-oleate, and N-tallow-trimethylene diamine dioleate were subjected to the water drop corrosion test described by Baker and Zisman in Ind. Eng. Chem., 41, 137 (1949).

The static water drop corrosion test as adapted consisted of immersing a polished test coupon of S. A. E. 1020 steel in an inhibited oil, allowing one hour for thermal and adsorption equilibria to be attained. A drop of water (0.2 ml.) was then placed in a cup-like depression in the test coupon by means of a capillary pipet. The test coupon remained immersed in the oil during this operation. The coupon remained undisturbed at the test temperature (140 F.) for 48 hours. At the end of this period the coupons were inspected for visible signs of corrosion. If there were any indications of rusting,- staining or pitting the test was classed as having failed. In each case the oil used as the solvent for the inhibitor was U. S. P. light white mineral oil. In replicate tests it was found that as little as .015 percent by weight ofboth N-tallow-trimethylene diamine mono and dioleates inhibited the oil sufiiciently so that it passed the test. The point at which significant failure of corrosion inhibition was noted for these two compounds was about .008 percent by weight. Good results were also obtained with N-talloW-methylene diamine, and no significant failure was noted down to about 0.125 weight percent. It is particularly noteworthy that the effective concentrations 0.015 weight percent of the fatty acid-amine salts tested are considerably smaller than the concentrations normally required for effective corrosion inhibition.

Example I] The duration of the static water drop corrosion test was lengthened to 168 hours. Various concentrations of N-tallow-trimethylene diamine mono and dioleates in hydrocarbon oils were subjected to the longer period of testing.

employed in the test. It was found that rusting of the coupons in hydrocarbon oils inhibited with less than 0.01 weight percent of the diamine oleates occurred in 15 to 30 minutes. This was also the time required for rust to appear on the coupons immersed in uninhibited oils. If, however, as the weight percent of the inhibiting agents in the oils were increased to about .015 weight percent, there was no corrosion after 168 hours of testing. In other words, if rusting did not occur within the first half hour of the test, the anti-corrosion effect was greatly prolonged. This would seem to be strong evidence for the Uninhibited hydrocarbon oils of the same type were also tested. The test coupons were observed through a window in the constant temperature cabinet which was planar crystal theory and other of the theoretical cons'idcrations discussed above.

Example III Amild steel coupon was immersed in a 0.2 weight percent solution of N-tallow-trimethylene diamine oleates in petroleum ether and allowed to stand for 30 minutes. The coupon was then removed and the solvent evaporated. A drop of water placed on the coupon caused rusting in approximately .the same length of time as required for rusting on a control coupon. When, however, a nonvolatile, non-polar solvent, such as white mineral oil was employed as .theliquid carrier for the inhibiting agents, there was no rusting in the time required for several water drops to evaporate, whereas control coupons treated with uninhibited oil rusted inl5 to 30 minutes.

Example IV Test coupons which have been used in the static water drop corrosiontest of Example II were removed from theinhibited oils and excess oil removed with a dry cloth to facilitate inspection for rusting, staining or pitting. These coupons were then set aside, and stored in contact with the atmosphere. Several months later it was noted that the coupons which had been in the N-tallow-trimethylene diamine oleate inhibited oils were completely free of corrosion as compared with other coupons which showed varying stages of corrosion. It was also noted that those coupons which had been in the inhibited oils could not be stained by fingerprints.

.The test and reported observations in Examples III and IV indicate that the solvent has a definite function in the protection of the metal surfaces by the inhibiting agents of this invention. The possible mechanism of this cooperative action between the solvent and the inhibiting agents has been discussed above. When the metal surface is normally exposed to the atmosphere, the cooperative actionsbetween the treating agent and the liquid carrier used to form the film of the inhibiting agent on the metal surface reaches a maximum when the liquid carrier or solvent is of the non-polar type and of low volatility. However, it was also found that some cooperation of the type described exists between the inhibiting agents of the invention and polar solvents such as ethyl alcohol When such solvents containing the dissolved inhibiting agents are continuously in contact with the metal surfaces.

While in the foregoing specification there has been set forth specific embodiments of this invention for purpose of illustration, it will be'apparent to those skilled in the art that many of the specific embodiments and details thereof can be varied widely without departing from the spirit of this invention.

-We claim:

1. The method of inhibiting corrosion of a ferrous metal surface, comprising forming an adsorbed protective film on said metal surface of the salt reaction product of a polyamine compound with an acid, said polyamine compound containing at least .2 amine groups in its molecular structure connected by a polymethylene group having from 2 to 6 methylene groups, one of said amine groups being connected to a radical selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said polyamine compound to form a salt thereof being selected from the group consisting of fatty and rosin acidscontaining from 6 to 22 carbon atoms.

2. The method of inhibiting corrosion of a ferrous inetalsurface, comprising forming an adsorbed protective film on said metal surface of the salt reaction product ofa polyamine compound with an acid, said polyamine compound including in its molecular structure at least ,2 amine'groups connected by the trimethylene group, one of said amine groups being connected to a radical selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 .to 22 carbon atoms and alicyclic radicals derived from the rosin acids, said acid reacted with said polyamine compound to form a salt thereof being selected from the group consisting .of fatty and rosin acids havingfrom 6 to 22 carbon atoms.

3. The method of inhibiting corrosion of a metal surface, comprising dissolving at least .01 percent by weight of the salt reaction product of a diamine and an acidin a non-polar solvent, said diamine including in its molecular structure a trimethylene group extending between said amine groups and having one of its amine groups connected to a radical selected from the group consisting of aliphatic radicals derivedfrom fatty acids having .from 8 to 22 carbon atoms and alicyclic radicals derived from ".sin acids, said acid reacted with said diamine to form a salt thereof being selectedfrom the groupconsistingof fatty and rosin acids containing from 6 to 22 carbon atoms, and then contacting said metal surface with said solvent containing said reaction product to deposit a protective film thereon of said reaction product.

4. The method of inhibiting corrosion of a ferrous metal surface, comprising dissolving at least .015 percent by weight of .the salt reaction product of a diamine and an acid in a hydrocarbon oil, said diamine having a trimethylene group extending between the amine groups therein and having a fatty acid radical containing from 14 to 18 carbon atoms attached to one of the amine groups therein, said acid reacted with said diamine to form a salt thereof being selected from the group consisting of fatty and rosin acids containing from 6 to 22 carbon atoms, and then contacting said ferrous metal surface with said hydrocarbon oil containing said reaction product to deposit a protective film thereon over said reaction product, whereby molecules of said hydrocarbon oil are also incorporated in said protective film.

5. The method of inhibiting corrosion of a ferrous metal surface, comprising dissolving at least .01 percent by weight of an N-tallow-trimethylene diamine oleate in a non-polar solvent, and then contacting a ferrous metal I surface with said solvent containing said oleate to deposit a protective film thereon of said oleate.

6. The .rnethod of inhibiting corrosion of a ferrous metal surface, comprising dissolving at least .015 percent by weight of an N-tallow-trimethylene diamine oleate in a hydrocarbon oil, and then contacting a ferrous metal surface with said oil containing said oleate to deposit a protective film thereon of said oleate, whereby molecules of said hydrocarbon oil are also incorporated in said protective film.

7. The method of inhibiting corrosion of a ferrous metalsurfacegnormally exposed to the corrosive action of .theatmosphere, comprising dissolving at least 0.1 percent by weightof an .N-tallow-trimethylene diamine oleate in a non-polar solvent of low volatility ,to form a protective treating solution, and then.applying'saidztreating surface to 'a ferrous metal surface to "form aifilm thereon containing molecules of said solvent in closely bound association with the molecules of said oleate, and then exposing said metal'surface to the atmospherewith said protective film thereon.

8. A composition for use in controlling corrosion of metal surfaces, comprising a protective hydrocarbon oil having dissolved therein at least .01 percent by weight of the salt reaction product of a diamine compound with an acid, said diamine compound having a trimethylene group extending between the amine groups therein and having a radical connected to one of the amine groups selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said diamine compound to form a salt thereof being selected from the group consisting of fatty and rosin acids having from 6 to 22 carbon atoms.

9. A composition for use in controlling corrosion of metal surfaces comprising, a protective hydrocarbon oil having dissolved therein at least 0.015 percent by weight of an N-tallow-trimethylene diamine oleate.

10. A composition for use in controlling corrosion of metal surfaces, comprising a protective hydrocarbon grease containing at least 1 percent by Weight of the reaction product of a diamine and an acid, said diamine including a trimethylene group extending between the amine groups therein and having a radical attached to one of the amine groups selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted With said diamine to form a salt thereof being selected from the group consisting of fatty and rosin acids having from 6 to 22 carbon atoms.

11. A composition for use in controlling corrosion of metal surfaces, comprising a protective grease composed mainly of a gelled hydrocarbon oil in admixture with at least 1 percent by Weight of an N-tallow-trimethylene diamine oleate.

12. The method of inhibiting corrosion of a metal surface, comprising dissolving at least .01% by weight of the salt reaction product of a polyamine compound with an acid in a hydrocarbon oil, said polyamine compound containing at least 2 amine groups in its molecular structure connected by a polymethylene group having from 2 to 6 methylene groups, one of said amine groups being connected to a radical selected from a group consisting of aliphatic radicals derived from fatty acids having from 3 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said polyamine compound to form a salt thereof being selected from the group consisting of fatty and rosin acids containing from 6 to 22 carbon atoms.

13. A composition for use in controlling corrosion of metal surfaces, comprising a protective hydrocarbon oil having dissolved therein at least .0l% by weight of the salt reaction product of a polyamine compound with an acid, said polyamine compound containing at least 2 amine groups in its molecular structure connected by a polymethylene group having from 2 to 6 methylene groups, one of said amine groups being connected to a radical selected from a group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said polyamine compound to form a salt thereof being selected from the group consisting of fatty and rosin acids containing from 6 to 22 carbon atoms.

14. The method of inhibiting corrosion of a metal surface, comprising forming an adsorbed protective film on said metal surface of a polyamine compound including in its molecular structure at least two amine groups connected by a polymethylene group having from 2 to 6 methylene groups, one of said amine groups being connected to a radical selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids.

15. The method of inhibiting corrosion of a metal surface, comprising forming an adsorbed protective film on said metal surface of the salt reaction product of a polyamine compound with an acid, said polyamine compound containing at least 2 amine groups in its molecular structure connected by a polyrnethylene group having from 2 to 6 methylene groups, one of said amine groups being connected to a radical selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said polyamine compound to form a salt thereof being selected from the group consisting of fatty and rosin acids containing from 6 to 22 carbon atoms.

16. The method of inhibiting corrosion of a metal surface, comprising forming an adsorbed protective film on said metal surface of the salt reaction product of an N-alkyl-trimethylene diamine and a fatty acid, the alkyl group of said diamine containing from 14 to 18 carbon atoms, said fatty acid containing from 6 to 22 carbon atoms.

17. The method of inhibiting corrosion of a ferrous metal surface, comprising dissolving about .05 to .3% by Weight of the salt reaction product of an N-alkyl-trimethylene diamine and a fatty acid in a non-polar solvent, the alkyl group of said diamine containing from 14 to 18 carbon atoms, said fatty acid containing from 6 to 22 carbon atoms, and then contacting said ferrous metal surface with said solvent containing said reaction product to deposit a protective film thereon of said reaction product.

18. The method of inhibiting corrosion of a metal surface, comprising forming an adsorbed protective film on said metal surface of the salt reaction product of a polyamine with an acid, said polyamine compound including in its molecular structure at least two amine groups connected by a trimethylene group, one of said amine groups being connected to a radical selected from the group consisting of aliphatic radicals derived from fatty acids having from 8 to 22 carbon atoms and alicyclic radicals derived from rosin acids, said acid reacted with said polyamine compound to form a salt thereof being a carboxyhydrocarbon containing from 6 to 22 carbon atoms.

19. The method of claim 18 in which said polyamine compound is a trimethylene diamine compound, and in which said carboXy-hydrocarbon is an aliphatic carboxyhydrocarbon.

20. The method of claim 18 in which said polyamine compound is a trimethylene diamine compound, and in which said carboxy-hydrocarbon is an alicyclic carboxyhydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS 2,244,712 Kyrides Jan. 10, 1941 2,267,204 Kyrides Dec. 23, 1941 2,400,785 Rust May 21, 1946 2,532,277 Castle Dec. 5, 1950 2,564,422 Barnum Aug. 14, 1951 2,568,876 White et al. Sept. 25, 1951 2,638,450 White May 12, 1953 OTHER REFERENCES Frost et al.: Journal Drg. Chem., vol. 15, pages 51 to 53 (1950). 

1. THE METHOD OF INHIBITING CORROSION OF A FERROUS METAL SURFACE, COMPRISING FORMING AN ADSORBED PROTECTIVE FILM ON SAID METAL SURFACE OF THE SALT REACTION PRODUCT OF A POLYAMINE COMPOUND WITH AN ACID, SAID POLYAMINE COMOUND CONTAINING AT LEAST 2 AMINE GROUPS IN ITS MOLECULAR STRUCTURE CONNECTED BY A POLYMETHYLENE GROUP HAVING FROM 2 TO 6 METHYLENE GROUPS, ONE OF SAID AMINE GROUPS BEING CONNECTED TO A RADICAL SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC RADICALS DERIVED FROM FATTY ACIDS HAVING FROM 8 TO 22 CARBON ATOMS AND ALICYLIC RADICALS DERIVED FROM ROSIN ACIDS, SAID ACID REACTED WITH SAID POLYAMINE COMPOUND TO FORM A SALT THEREOF BEING SELECTED FROM THE GROUP CONSISTING OF FATTY AND ROSIN ACIDS CONTAINING FROM 6 TO 22 CARBON ATOMS.
 11. A COMPOSITION FOR USE IN CONTROLLING CORROSION OF METAL SURFACES, COMPRISING A PROTECTIVE GREASE COMPOSED MAINLY OF A GELLED HYDROCARBON OIL IN ADMIXTURE WITH AT LEAST 1 PERCENT BY WEIGHT OF AN N-TALLOW-TRIMETHYLENE DIAMINE OLEATE. 